1. Field of the Invention
The invention relates to a control system for a spark-ignition internal combustion engine.
2. Description of Related Art
A control system for an internal combustion engine including a tumble flow control valve that produces tumble flow in each cylinder is disclosed in, for example, Japanese Patent Application Publication No. 2012-021501 (JP 2012-021501 A). In this control system, an estimated tumble ratio is calculated, based on a detection value of a first air flow meter provided upstream of a throttle valve, and a detection value of a second air flow meter provided right below the tumble flow control valve. Then, the feedback control of the opening of the tumble flow control valve is performed so that the estimated tumble ratio thus calculated follows a target tumble ratio. The target tumble ratio is set to a value within a permissible control range established for avoiding misfiring and unstable combustion.